Varrak 说:
In my opinion, there could be some different policies special to certain government system, that will appear in policy list when such government system adopted. There could be 2-3 special policies connected to government systems. For example if the faction is totaliter militarist dictatorship, there wouldn't be a choice for liberal policies in policy list, and we would have to change government system first in order to unlock liberalist policies (make them appear in policy list).

According to that, a Kingdom (or faction, or whatever it's called) can either be a Monarchy, an Oligarchy or a Democracy, which presumably affects how power is transferred when a ruler dies or is otherwise deposed. Maybe the government type can be changed within the "policies" tab (the screenshot doesn't show us the first few options), if the clans support it? Or maybe different factions have different 'traditions' of government, and they can't be changed?
Specific policies or laws are either "Centralizing", "Legalist" or "Egalitarian", and the Kingdom Laws section in the encyclopedia suggest that they do vary in terms of which ones are available according to which government type you have.
I think it looks like the Khuzaits are a monarchy because the ruling clan is called "Urkhunait", and the Khuzait faction blog says this:
Urkhun imposed discipline on the unruly clans, forcing them to ride to war on his command instead of simply when they wished. But with the coming of statehood and its burdens, the spirit of unity was lost. Urkhun died, and though his descendants still rule the Khuzait Khanate, the other clans feel that they should be the ones to raise the nine-horsetail banner that symbolizes the supreme authority.
It's probably already very highly centralized, and not very legalistic or egalitarian; that's probably why there are several options in the policies screen we can see that would make it more legalistic and more egalitarian. Patriotism is probably a centralizing law; but the rest of them look like they would make the Khanate less centralized, less totalitarian, less dictatorial - probably because it's already near the limit of maximum centralization as it is.
So I reckon the available policies probably do change according to the type of government you have, as you suggest, but possibly not exactly in the way you suggest.